The present invention is directed to a device for delivery of medicament, and in particular to a jet injector with a short needle to reduce the pressure at which the jet injector must eject the medicament for proper delivery.
A wide variety of needleless injectors are known in the art. Examples of such injectors include those described in U.S. Pat. No. 5,599,302 issued to Lilley et al., U.S. Pat. No. 5,062,830 to Dunlap, and U.S. Pat. No. 4,790,824 to Morrow et al. In general, these and similar injectors administer medication as a fine, high velocity jet delivered under sufficient pressure to enable the jet to pass through the skin.
As the skin is a tissue composed of several layers and the injector is applied to the external surface of the outermost layer, the delivery pressure must be high enough to penetrate all layers of the skin. The layers of skin include, the epidermis, the outermost layer of skin, the dermis, and the subcutaneous region. The required delivery pressure is typically greater than approximately 4000 p.s.i. (measured as the force of the fluid stream divided by the cross-sectional area of the fluid stream).
Although this pressure is readily achievable with most injectors, there are some circumstances in which delivery of medicament to the subcutaneous region under a reduced pressure is desirable. For example, drugs that require a specific molecular structural arrangement, such as a linear protein configuration, may be rendered ineffective due to shear forces caused by the delivery of the drug at high pressures that alter the structural arrangement of the drug. As it is more difficult to deliver a large volume of fluid at a high pressure compared to a small volume, using a lower pressure facilitates delivery of a larger volume of fluid. Furthermore, the lower pressure could make manufacturing an injector device less expensive. The lower pressure would also reduce adverse stresses on the device and result in a corresponding increased useable device lifetime.
One of the advantages associated with jet injectors is the absence of a hypodermic needle. Given the aversion to needles possessed by some, the absence of a needle provides a psychological benefit. Even devices that utilize conventional hypodermic needles have attempted to capitalize on this psychological benefit. For example, self-injectors or auto-injectors like the ones disclosed in U.S. Pat. Nos. 4,553,962, 4,378,015 have retractable needles which are hidden until activation. Upon activation, the needle extends from the bottom of the device and penetrates the user""s skin to deliver medicament. As none of these devices involves delivery of the medicament using jet injection, the medicament delivery location is limited by the length of the needle. For example, if delivery in the subcutaneous region is desired, the needle must be long enough to reach the subcutaneous region. Furthermore, as auto-injectors operate like syringes, the injection time is several seconds or longer. In contrast, jet injectors typically inject in fractions of a second.
Thus, there exists a need for a jet injector with a short needle to reduce the pressure at which the jet injector must eject the medicament for proper delivery.
The present invention relates to a needle assisted jet injector. In one embodiment, the injection device includes a housing; a nozzle assembly defining a fluid chamber, having an opening for slidingly receiving at least a portion of the needle and removably associated with the housing; a plunger movable in the fluid chamber; a trigger assembly; an energy generating source operatively associated with the trigger assembly so that movement of the trigger assembly activates the energy source to move the plunger in a first direction to expel a fluid from the fluid chamber; and a retractable injection-assisting needle at a distal end of the injector. The retractable injection-assisting needle has a needle tip located at a distal end of the needle with at least a portion configured and dimensioned to slide through the nozzle assembly opening; a discharge channel within the needle tip and terminating in an orifice through which the fluid is expelled; a body portion to direct fluid towards the discharge channel; a plunger receptor configured and dimensioned to receive at least a portion of the plunger; and a retraction element operatively associated with the nozzle assembly. The needle is located within the nozzle assembly in a retracted position prior to activation of the energy source. Movement of the plunger in the first direction upon activation of the energy source results in at least a portion of the needle tip extending beyond the nozzle assembly opening and the retraction element returns the needle tip to the retracted position after activation of the energy source.
The retraction element can be a resilient O-ring, a spring, or a flexible membrane which moves to allow extension of the needle tip beyond the nozzle assembly opening and then returns to its original position to return the needle tip to its retracted position. The needle body can have an exterior surface which includes a ridge or recess for accommodating the retraction element. A shoulder can be disposed between the needle tip and the needle body for accommodating the retraction element. Preferably, the needle tip has a length of approximately 1-5 mm.
In another embodiment, the injector has a non-retracting fixed needle. The injection-assisting needle comprises a body fixed to a distal end of the nozzle assembly and a discharge channel extending through the needle body, in fluid communication at a first end with the fluid chamber, and terminating at a second end in an orifice through which the fluid is expelled. Preferably, the body has a length of approximately 1-5 mm.
The present invention also relates to a method of delivering medicament to an injection site of a patient. The method includes the steps of: inserting a needle into a needle insertion point, said needle having a length less than 5 mm and being operatively associated with an orifice in a nozzle assembly in fluid communication with an ampule chamber containing the medicament; activating an energy mechanism; and coupling a pressure wall member disposed and movable within the ampule chamber to the activated energy mechanism to move the pressure wall member at a speed sufficient to eject the medicament from the ampule chamber through the orifice and needle under a pressure which is sufficient to deliver a substantial portion of the medicament to the injection site. The needle insertion point is located more superficial than the injection site.
The method preferably includes the steps extending a needle from a shield prior to inserting the needle into the needle insertion point and then retracting the needle into the shield after the medicament has been delivered to the injection site.